My drawing is a bit too crammed with lines and arcs to make it easy to follow each step from the beginning.

This link shows, first, how to bisect a line, while at the same time drawing a line perpendicular to another. That was my first step to get my four quadrants. Next it shows how to bisect an angle. That's how I got my 45d angle:http://en.wikipedia.org/wiki/Bisection